In an effort to economically develop oil and/or gas producing reservoirs, the Petroleum Industry relies heavily upon educated predictions of reservoir conditions utilizing technologies available for reservoir characterization prior to making enormous investments into the drilling and completing of wells. Evaluating known data from similar reservoirs as well as actual data obtained from exploratory wells or other early development efforts can greatly enhance the industries ability to optimize the development and management of a hydrocarbon-producing field. Hydrocarbon recovery modeling using sophisticated computer simulation of reservoir processes and physical characteristics has become a critical evaluation tool for effective and economical reservoir development and management.
Typically, hydrocarbon recovery modeling of reservoirs includes both fluid-dynamical modeling of multi-phase transport in permeable media, generally by numerical analysis methods incorporated into reservoir simulators, as well as geo-mechanical modeling that may utilize structural analysis software packages. Additionally, hydrocarbon recovery modeling can include material modeling of the physical properties of the reservoir's rock formations. Many software computer programs used for this modeling are generally available within the industry.
Reservoir simulators provide a tool that can be utilized by reservoir engineers to make predictions about the multi-phase flow of oil, gas, and water in underground hydrocarbon accumulations. Engineers can simulate various methods of producing oil fields, and can experiment with locations and design of wellbores to optimize both the recoveries of such resources as well as their own business profitability. Reservoir models use various laws, for example Darcy's law, to relate rock parameters such as porosity, absolute and relative permeability, and capillary pressure to quantify the pressure, flux and dissipation of a reservoir.
Geo-mechanical technologies characterize rock properties to predict the state of earth stresses and natural fractures and or faults in a formation. Geo-mechanical models are based on various laws, such as Hooke's law, to relate rock parameters such as elastic and plastic rigidity to quantify the displacement, stress and internal energy of a reservoir. Traditionally, geo-mechanical modeling of hydrocarbon reservoirs is evaluated at static reservoir conditions, such as pre-drilling reservoir conditions. Generally the evaluation is primarily focused on optimization of the actual drilling process, for example to design a drilling program that eliminates or minimizes mechanical instabilities in the borehole while drilling a well. As a result, much of the focus of the geo-mechanical studies is on weak shale sections or depleted reservoirs that tend to create drilling hazards.
In most situations in the petroleum industry, completions are designed to accommodate a given wellbore based upon reservoir drainage recommendations. These reservoir drainage models can be used to determine the most efficient drainage points within the reservoir and can also be used to evaluate the basic type of completion whether it is a horizontal wellbore, a deviated wellbore or a vertical wellbore. Using this approach the well planning is done to hit the desired drainage target and to minimize the development cost through proper placement of individual well locations or central drilling sites.
In many cases the hydrocarbon producing reservoirs exist in a normal fault regime where there is little directional preference for both wellbore stability or completion selection. As a result, they are quite forgiving to different completion options. There are, however, a number of regions around the world that are in more complex stress states, sometimes transitioning from a normal faulting regime to strike slip or even reverse fault conditions. When these conditions exist, there can be a very strong directional preference for optimum completion design. In those conditions proper alignment and placement of the wellbore based upon specific completion techniques can vastly improve the reliability and productivity of the wellbore.